1. Field of the Invention
The disclosures herein generally relate to a network quality measurement apparatus, a transmission apparatus, a reception apparatus, and a network quality measurement method for measuring the quality of communication in a network such as the Internet.
2. Description of the Related Art
As a result of the development of network technologies, there has been an increase in the use of real-time-system applications such as stream data delivery and VoIP (Voice Over Internet Protocol) for transmission and reception of audio and video data or the like between apparatuses. When a real-time-system application is used, the quality of audio and video reproduction by the application using received audio and video data is largely affected by network conditions. Because of this, network conditions need to be monitored for the purpose of coping with problems that may occur when the quality of reproduction drops during the system operation.
One way to monitor network condition is to provide an agent for transmitting a large number of measurement packets at constant intervals or in a manner similar to the occurrence pattern of user packets and another agent for receiving these measurement packets in a network. In this active measurement method, network quality between the agents is estimated based on the quality of communication of the measurement packets.
Audio quality may be calculated by use of a standard such as ITU standard ITU-G.107 defined by the ITU (International Telecommunication Union) or TTC standard JJ-201.01 defined by the TCC (Telecommunication Technology Committee). Video quality may be calculated by use of ITU standard ITU-T.241 (ITU-R BT.1720).
With an active measurement method that transmits measurement packets by mimicking the occurrence pattern of user packets, a large number of measurement packets end up being sent in addition to user packets. This gives rise to a problem in that the load on the network increases.
In real-time-system applications such as VoIP and stream delivery, audio and video data to be transmitted are divided into pieces of predetermined unit size, which are then transmitted at predetermined intervals (e.g., 20 ms). When a plurality of terminal apparatuses coincide with each other in terms of their data transmission timing, the load on the network may exhibit periodical imbalances if these apparatuses uses the same network at the same time. As a result, network quality such as the quality of telephone call may fluctuate.
FIG. 1 is a drawing showing an example of timing of packet transmission. In this example, VoIP packets are transmitted at transmission interval Ts. Transmission interval Ts may be 20 ms, for example.
A phone call A always uses the first half of VoIP packet transmission interval Ts for transmission of VoIP packets PA. On the other hand, a phone call B always uses the second half of VoIP packet transmission interval Ts for transmission of VoIP packets PB.
When there is an increase in the number of calls utilizing similar transmission timing to the phone call A, the traffic of phone calls increases in the first half of VoIP packet transmission interval Ts, thereby bringing about periodic imbalances in the load L on the network. The interval of imbalances in the load L on the network is equal to the VoIP packet transmission interval Ts. Accordingly, the transmission of VoIP packets PA at such transmission timing as used by the phone call A results in the delay of VoIP packets PA or the loss of VoIP packets PA. This causes a drop in communication quality.
In order to measure network quality (i.e., the degree of imbalances in network load) at multiple points (i.e., multiple points in time) within the data transmission interval, a plurality of agents need to be used, and also need to be synchronized with each other in terms of the timing of measurement packet transmission. This is because each agent has fixed transmission timing for transmitting measurement packets. This arrangement is cumbersome.
In order to obviate these two problems described above, Japanese Patent Application Publication No. 2007-208327 discloses a method that completes the measurement of network load (i.e., density distribution defined as variation in the network load over time) at multiple points within the data transmission interval by use of a single agent through a single collection of data. This is done by slightly increasing and decreasing the transmission intervals of measurement packets relative to the data transmission interval.
The measurement method disclosed in the above-noted patent document neither increases network load nor requires the synchronization of measurement packet transmission between multiple agents. This method, however, collects data for multiple points within the data transmission interval, and does not focus attention on a particular point where quality degradation may likely occur. Because of this, this method may not be able to immediately detect degradation in network quality when it happens.
It may thus be desirable to provide a network quality measurement apparatus, a transmission apparatus, a reception apparatus, and a network quality measurement method that can immediately detect degradation in network quality without increasing network load and without the need to establish synchronization of measurement packet transmission between multiple agents.